Negative resist composition, a method for forming a resist pattern thereof, and a method for fabricating a semiconductor device

ABSTRACT

A negative resist composition containing an alkaline-soluble resin as a base material, in which an oxetane structure represented by the following formula (1):  
                 
is contained in a structure of the alkaline-soluble resin or in a structure of a compound used in combination with the alkaline-soluble resin, is disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

The present invention is a continuation-in-part application of the U.S.patent application Ser. No. 09/785,306 filed on Feb. 20, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the art of microfabricationof semiconductor devices, more particularly, to a negative resistcomposition that can be developed with a basic aqueous solution withoutcausing swelling, a method for forming a fine resist pattern thereof anda method for fabricating a semiconductor device. According to thepresent invention, a resist material having a lower absorbance and ahigh sensitivity for shorter wavelength radiation and high dry etchingresistance can be provided. Thus, a semiconductor integrated circuitsuch as VLSI and ULSI etc., as well as other devices needingmicrofabrication such as a magnetic resistive head, and the like, can beadvantageously fabricated.

2. Description of the Related Art

A photolithography technique using krypton fluoride excimer laser(wavelength: 248 nm, as referred to KrF hereinafter) has been dominatingfor mass production of highly miniaturized semiconductor devices due toavailability of chemical amplification type resist such as the oneproposed by H. Ito, et al. For example, reference should be made to J.M. J. Frechet et al., Proc Microcircuit Eng., 260 (1982), H. Ito et al.,Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86(1983), H. Ito et al., “Polymers in Electronics”, ACS Symposium Series242, and T. Davidson et al., ACS, 11 (1984), U.S. Pat. No. 4,491,628(1985).

Recently, in relation to fabrication of a higher integrated circuitdevices such as Gbit DRAMs, a lithography technique using ArF (Argonfluoride) excimer laser (wavelength: 193 nm) has been actively studied,wherein the ArF excimer laser emits a shorter wavelength radiation ascompared with the KrF excimer laser. Since conventional phenol resinshave a strong optical absorbance at such shorter wavelengths, the resinmaterial constituting the base of the resist has to be changed. Thus,there is an urgent need of developing a resist material applicable forsuch shorter wavelength radiations.

As a chemical amplification type resist applicable for the wavelength ofArF radiation, positive resists have been actively studied (see, forexample, K. Nozaki et al., Chem. Mater., 6, 1492 (1994), K. Nakano etal., Proc. SPIE, 2195, 194 (1994), R. D. Allen et al., Proc. SPIE, 2438,474 (1994), Japanese Laid-Open patent application No. 9-90637, K. Nozakiet al., Jpn. J. Appl. Phys., 35, L528 (1996), and K. Nozaki et al., J.Photopolym. Sci. Technol., 10(4), 545-550 (1997)).

However, there are few reports about single layer negative chemicalamplification type resists. Most of the resists are cross-linking typeresists.

For example, as described in A. Katsuyama et al., Abstracted Papers ofThird International Symposium on 193 nm Lithography, 51 (1997), or inMaeda et al., Abstracts of the 58^(th) Japan Society of Applied PhysicsNo. 2, 647 (3a-Sc-17) (1997), or in T. Naito et al., Proc. SPIE, 3333,503 (1998), Japanese Laid-Open patent application No. 2000-122288, or inJapanese Laid-Open patent application No. 2000-147769, a cross-linkingtype resist is utilized for patterning, there is a report ofcross-linking type resist in which there is caused a difference ofsolubility to a developer between an exposed area and an unexposed areaby increasing the molecular weight as a result of cross-linking reactionat the exposed area. However, such an approach cannot avoid the problemof swelling of the exposed patterns, and the use thereof in the art ofmicrofabrication of semiconductor devices is rather limited.

Recently, there is a report of a single-layer negative chemicalamplification type resist that uses a polarity change, which in turn iscaused by an intra-molecular lactonization that uses a hydroxycarboxylicacid structure (for example, reference should be made to Y. Yokoyama etal., J. Photopolym. Sci. Technol., 13(4), 579 (2000)). Further, there isa report of a single-layer negative chemical amplification resist thatuses a pinacol rearrangement (for example, reference should be made toS. Cho et al., Proc. SPIE, 3999, 62 (2000)).

However, in the case of using the intra-molecular lactonization, thereis a problem in that proportion of the polarity change is relativelysmall and it is difficult to perform patterning with high contrast.Also, in the case of the pinacol rearrangement, there are problems suchas adhesion property to a substrate due to the inclusion of fluorine andpreservation stability caused as a result of inclusion of maleicanhydride.

Thus, the resist utilizing pinacol arrangement has not been established.Although the inventors previously developed a single-layer negativechemical amplification type resist using polarity change that uses aninter-molecular protection reaction (Japanese Laid-Open patentapplication No. 11-311860 and No. 11-305436), there was a problem thatno enough reactivity was achieved because of the fact that the reactionis an inter-molecular reaction.

A negative resist can be advantageously used when it is difficult toproduce a mask with a positive resist or when the exposed area is smallas in the case of the gate of a transistor, due to the fact that theunexposed area of the resist is dissolved. Further, the use of such anegative resist is advantageous also in the case of forming a phaseshift mask used in the technology of super-resolution exposure forobtaining a resolution equal to or less than the wavelength used for theexposure, and also in the Levenson mask, which is used for enhancingoptical images.

Thus, a negative resist is hoped for also in the art of ArF exposure.These masks formed of the negative resist are considered also as beingapplicable to the case in which the resolution of equal to or less than130 nm is required in combination with the use of ArF excimer radiationsource. Thus, there is an urgent demand for a resist capable ofresolving such a fine pattern without causing swelling.

Meanwhile, with increase of integration density of semiconductordevices, the number of interconnection layers is increasing also inaddition to the miniaturization of the line width. In relation to such ademand, the requirement imposed to a resist material for lithographicprocess is becoming stringent every year. In addition to the resolution,the dimensional accuracy after etching has emerged recently as animportant factor of a resist material. With the shifting of the exposurewavelength to a shorter side, it is expected that there appeardifficulty in keeping up a sufficient transparency for the resistmaterial. Thus, it is expected that the thickness of the resist layerbecomes thin in such a future resist material. When the thickness of theresist layer is thus reduced, the etching property of the resist layerbecomes a paramount problem in the fabrication process of miniaturizedsemiconductor devices. Similar problems appear also in the case offabricating any highly miniaturized devices that use a highlyminiaturized photolithographic patterning process such as thefabrication process of magneto-resistive heads for use in high-densitymagnetic recording.

Meanwhile, there is a proposal of surface imaging technique as aneffective technology solving the foregoing problems. Particularly, thereis a proposal of bilayer resist process that uses a resist compositioncontaining silicon. The bilayer method comprises the steps of forming alower resist layer by applying a solution containing an organic resinwith a thickness of about 0.5 μm, followed by formation of an upperresist layer on the lower resist layer thus formed, with a thickness ofabout 0.1 μm. Next, the upper resist layer is patterned by an exposureand developing process to form a upper resist pattern, and the lowerresist layer is subjected to an etching process by using the upperresist pattern as a mask. According to such a process, it becomespossible to form a resist pattern having a high aspect ratio.

The resist material for use in such a bilayer method is required tosatisfy various requirements such as excellent exposure resolution,excellent storage stability, capability of being developed by basicaqueous solutions (alkaline developability), in other words, in additionto excellent resistance to oxygen reactive etching (hereinafter referredto as O₂-RIE). At the present stage, however, there is no commerciallyavailable resist material that satisfies all of the above requirements.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful negative resist composition wherein the foregoingproblems are eliminated.

Another and more specific object of the present invention is to providea negative resist composition capable of forming fine, miniaturizedpatterns, having a practical optical sensitivity against shortwavelength radiations, and being developed by a basic aqueous solutionwithout causing swelling.

Another object of the present invention is to provide a resistcomposition capable of being exposed by an exposure radiation having awavelength in the deep ultraviolet region, such as the one produced by aKrF excimer laser or an ArF excimer laser, while maintaining excellentdry etching resistance.

Another object of the present invention is to provide a high-sensitivityresist composition capable of providing fine patterns whilesimultaneously providing high contrast and high resolution, byincreasing the polarity difference between at an exposed area and anunexposed area.

Another object of the present invention is to provide a high-sensitivityresist composition having a high O₂-RIE resistance and capable of beingdeveloped by a basic aqueous solution, so that the resist composition isapplicable for the formation of the upper layer resist film in amulti-layer resist process.

Another object of the present invention is to provide a method offorming a resist pattern using such resist composition.

Another object of the present invention is to provide a method forfabricating a semiconductor device by using such resist composition asfor the pattern formation material.

Another object of the present invention is to provide a negative resistcomposition containing an alkaline-soluble resin as a base material, inwhich an oxetane structure represented by the following formula (1):

is contained in a structure of the alkaline-soluble resin or in astructure of a compound used in combination with the alkaline-solubleresin.

Another object of the present invention is to provide a method offorming a negative resist pattern comprising the steps of:

applying a resist composition on a substrate to form a resist film, theresist composition containing an alkaline-soluble resin as a basematerial, in which an oxetane structure represented by the followingformula (1):

is contained in a structure of the alkaline-soluble resin or in astructure of a compound used in combination with the alkaline-solubleresin;

exposing the resist film to radiation for imaging selectively;

developing the exposed resist film with a basic aqueous solution to formthe negative resist pattern.

Another object of the present invention is to provide a method forfabricating a semiconductor device comprising the steps of:

applying a resist composition on a substrate to form a resist film, theresist composition containing an alkaline-soluble resin as a basematerial, in which an oxetane structure represented by the followingformula (1):

is contained in a structure of the alkaline-soluble resin or in astructure of a compound used in combination with the alkaline-solubleresin;

exposing the resist film to radiation for imaging selectively;

developing the exposed resist film with a basic aqueous solution to forma negative resist pattern.

Another object of the present invention is to provide a method forforming a negative resist pattern comprising the steps of:

applying a first resist composition on a substrate to form a lower layerresist film;

applying a second resist composition on the lower layer resist film toform an upper layer resist film, the second resist compositioncontaining an alkaline-soluble resin as a base material, in which anoxetane structure represented by the following formula (1):

is contained in a structure of the alkaline-soluble resin or in astructure of a compound used in combination with the alkaline-solubleresin;

exposing the upper layer resist film to radiation for imagingselectively;

developing the exposed upper layer resist film with a basic aqueoussolution to form a resist pattern;

etching the lower layer resist film by using the resist pattern as for amask to form the negative resist pattern through the lower resist filmand the upper resist film.

Other objects and further features of the present invention will becomeapparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the result of an O₂-RIE resistance test in abilayer resist process conducted by using a resist composition accordingto the present invention; and

FIGS. 2A through 2C are diagrams showing the process steps of forming awiring pattern while using the resist composition of the presentinvention sequentially.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Principle]

The inventors actively studied in order to solve the problems describedabove. As a result, the inventors have found that, in a chemicalamplification type resist composition that uses, as a base resin, apolymer having an alkaline-soluble group and thus forming a film solubleto a basic aqueous solution, it is effective to introduce an oxetanestructure to the alkaline-soluble polymer or to a compound used incombination with the alkaline-soluble polymer.

Another object of the present invention is to provide a negative resistcomposition comprising an alkaline-soluble resin as for a base resin,wherein the alkaline-soluble resin or a compound used in combinationwith the alkaline-soluble resin contains an oxetane structurerepresented by the following formula (1).

Preferably, the resist composition is provided in the form of a chemicalamplification type resist. Thus, the resist composition according to thepresent invention may also include a photoacid generator that producesan acid reactive to the oxetane structure when the photoacid generatoris exposed to a radiation at the time of an imaging process. Thereby,although the resist composition itself is soluble to a basic aqueoussolution, after it is exposed to radiation for imaging, an exposed areaon the resist composition become alkaline-insoluble and can be developedby using a basic aqueous solution. While the amount of the photoacidgenerator depends on the acid strength of the acid generated after it isexposed to the radiation emitted from an exposure source, the amount ispreferably within the range from 0.1 to 50% by weight (percentagerelative to weight of a polymer) and more preferably within the rangefrom 1 to 15% by weight.

An alkaline-soluble polymer used as for a substrate resin is preferablya polymer containing at least one kind of substituent selected from thegroup consisting of a carboxyl group, a phenolic hydroxyl group, aN-hydroxyamide group, an oxime group, an imide group, a1,1,1,3,3,3-hexafluorocarbinol group represented by the formula (2),

and a sulfonic acid group in order to obtain alkaline solubility atdesired level.

At least one monomer unit constituting the alkaline-soluble polymer ispreferably a monomer unit having an acrylate-based monomer unit, amethacrylate-based monomer unit, a vinylphenol-based monomer unit, anN-substituted maleimide-based monomer unit, a styrene-based monomerunit, or a monomer unit having a polycyclic alicyclic hydrocarbon groupcomprising a plurality of ring structures represented by norbornene. Amonomer unit having a structure represented by an adamantyl group or anorbornyl group, etc. in the polycyclic alicyclic hydrocarbon group ismore preferable.

If the alkaline-soluble polymer is a copolymer, a monomer unitpolymerized with the monomer unit having an alkaline-soluble group mayhave any structure as far as the polymer maintains the nature ofalkaline solubility to a developer. Further, if the alkaline-solublepolymer is a three-component polymer, the monomer unit having analkaline-soluble group may be combined with two kinds of monomer unitshaving any structures as far as the polymer maintains the alkalinesolubility to a developer, similarly to the case described above.Further, combination of the three kinds of monomer units is alsopreferable. In these case, the polymer may contain not only a firstmonomer unit having an alkaline-soluble group but also a second monomerunit having an alkaline-soluble group and the combination of the twokinds of monomer units is also preferable.

In the alkaline-soluble polymer according to the present invention, thecontent of the monomer units having the alkaline-soluble group in thepolymer is not limited as far as the polymer itself exhibits properalkaline solubility. However, from the viewpoint of attaining apractical rate of dissolution to an alkali solution (rate of dissolutionagainst 2.38% TMAH developer of about from 100 angstrom/s to 1000angstrom/s), it is preferable to set the content of a monomer unithaving an alkaline-soluble group in the range from 5 to 95 mol %, morepreferably from 30 to 70 mol %, provided that the polymer consists oftwo or more monomer components. If the monomer content is less than 5mol %, no satisfactory patterning can be achieved because ofinsufficient alkaline-solubility in the case the alkaline-soluble grouphas weaker acidity than the carboxyl group. On the other hand, if thecontent is more than 95 mol %, the rate of dissolution to a basicaqueous solution is too fast in the case the alkaline-soluble group hasstronger acidity than a carboxyl group, and the patterning becomesdifficult because of the too large solubility. Therefore, it isdesirable to control the content of the monomer unit properly, dependingon the acidity of the alkaline-soluble group.

In one aspect of the present invention, it is preferable that analkaline-soluble polymer itself has an oxetane structure therein. Inthis case, the content of the monomer unit having an oxetane structurein the polymer is not limited as far as the polymer resin itselfexhibits proper alkaline-solubility. However, it is desirable to controlthe rate of the dissolution the polymer to the 2.38% TMAH developer tothe range of 0 to 40 angstrom/s at the exposed areas after thepost-exposure baking (PEB) process. For example, in the case of thepolymer consisting of two or more monomer components, the content of themonomer unit having an oxetane structure is preferably from 5 to 95 mol%, more preferably from 30 to 70 mol %.

According to another aspect of the present invention, it is preferableto combine a compound having an oxetane structure therein with analkaline-soluble polymer in the resist composition. In this case,although the content of the compound significantly depends on rate ofdissolution of the polymer against an alkali solution, it is recommendedto use a polymer content of 1 to 80% by weight, and more preferably from10 to 40% by weight (percentage to the weight of the polymer) in thecase the polymer has the above mentioned proper rate of dissolutionagainst the alkali solution.

In the resist composition according to the present invention, thealkaline-soluble resin used as for a base resin is preferably asilicon-containing resin in view of another aspect of the presentinvention. The silicon-containing resin also has at least onesubstituent selected from the group consisting of a carboxyl group, aphenolic hydroxyl group, and a hexafluorocarbinol group represented bythe above formula (2).

The silicon-containing resin preferably includes an oxetane structuretherein. The silicon-containing resin including an oxetane structure andis suitable for the base resin is preferably a silicon-containingpolymer represented by the following formula (3) or (4).

In the above formulae (3) and (4), p, q and r are positive integersrespectively.

In yet another aspect, the alkaline-soluble resin used as for the baseresin may be combined with a compound having an oxetane structure. Thecompound having the oxetane structure is preferably a silicon-containingresin represented by the following formula (5).

In the above formula (5), n is a positive integer.

The alkaline-soluble polymer for the base resin noted above haspreferably a weight-averaged molecular weight of 2,000 to one million,more preferably from 3,000 to 50,000, although the molecular weight mayvary widely with the composition and the desired effect of the resistcomposition.

The resist composition according to the present invention is preferablyprovided in the form of a solution in which the composition is dissolvedin a solvent selected from the group consisting of ethyl lactate, methylamyl ketone, methyl-3-methoxypropionate, ethyl-3-ethoxypropionate,propylene glycol methyl ether acetate, and a mixture thereof. The resistsolution may also contain a solvent selected from the group consistingof butyl acetate, γ-butyrolactone, propylene glycol methyl ether, and amixture thereof as for a supplementary solvent if necessary. Althoughthe supplementary solvent added to the resist solution may not berequired depending on the solubility of the solute, the amount of thesupplementary solvent added to a main solvent is generally in the rangefrom 1 to 30% by weight when a solute having low solubility is employed.The range of 10 to 20% by weight is more preferable.

Also, in order to obtain satisfactory patterning performance, it isdesirable that the absorbance of the resist composition is equal to orless than 1.75 at the spectral region (from 157 to 300 nm) of theradiation generated from an exposure source.

In another aspect of the present invention, the present inventionprovides a method of forming a negative resist pattern using the resistcomposition according to the present invention. With respect to themethod for forming a resist pattern, the resist composition according tothe present invention may be used in a single-layer resist process and amulti-layer resist process such as the bilayer resist process ortriple-layer resist process.

A method for forming a resist pattern according to the present inventioncomprises the steps of: applying the resist composition according to thepresent invention on a substrate to form a resist film; exposing theresist film to radiation for imaging selectively; developing the exposedresist film with a basic aqueous solution to form a negative resistpattern.

Also, when a multi-layer resist method is carried out, a method forforming a resist pattern according to the present invention comprisesthe steps of: applying a first resist composition on a substrate to forma lower layer resist film; applying the resist composition according tothe present invention on the lower layer resist film to form an upperlayer resist film; exposing the upper layer resist film to radiation forimaging selectively; developing the exposed upper layer resist film witha basic aqueous solution to form a resist pattern; etching theunderlying lower layer resist film by using the resist pattern as for amask; forming a negative resist pattern consisting of the lower layerresist film and the upper layer resist film thereon.

In the method of forming the resist pattern according to the presentinvention, a resist film formed on a substrate preferably undergoesheating treatment before and after the resist film is subjected to theselective exposure process. That is, in the method according to thepresent invention, the resist film is subjected to a pre-bake treatmentbefore the exposure process, wherein it is further preferable that theresist film is subjected to a post-bake treatment (aforementioned PEB)after the exposure process but before the development process.

In the method of forming a resist pattern according to the presentinvention, a radiation capable of inducing dissociation of the photoacidgenerator contained in the resist composition is employed as forradiation for the exposure process.

Further, a basic aqueous solution used as for a developer is preferablyan aqueous solution containing a metal hydroxide, in which the metal isclassified to I group or II group in the periodic table, such aspotassium hydroxide. Alternatively, the basic aqueous solution may bethe one containing an organic base but a metal ion such astetraalkylammonium hydroxide, etc. More preferably, the basic aqueoussolution may be an aqueous solution of tetramethylammonium hydoxide(TMAH). An additive such as a surfactant may be added to the basicaqueous solution so as to improve the development effect.

Another aspect of the present invention is to provide a method ofproducing a semiconductor device comprising of the step of forming theresist pattern described above.

First Embodiment

A negative resist composition according to the present invention ischaracterized by an oxetane structure represented by the above formula(1) contained in the structure of an alkaline-soluble resin used as fora base resin or in the structure of a compound used in combination withthe alkaline-soluble resin. Although it is known that a compound havingan oxetane structure itself can be utilized as for a photocurablecoating material (see Japanese Laid-Open Patent Application No.6-16804), the present invention is characterized by an oxetane structureintroduced into the alkaline-soluble resin having excellent dry-etchingresistance as a side-chain, or into a compound containing an oxetanestructure. According to the present invention, it was found that aresist material particularly suitable for microfabrication ofsemiconductor devices and the like, can be provided by using an oxetanestructure.

As for the behavior of the oxetane structure in the resist compositionof the present invention, the oxetane structure is subjected to aring-open reaction under a certain condition, and the oxetane structurethus experienced the ring-open reaction causes a reaction with analkaline-soluble group such as hydroxyl group, carboxyl group, and thelike. The alkaline-soluble group is lost after the reaction, and theexposed area on the resist film becomes alkaline-insoluble. Thus, anegative pattern is formed after a development process conducted byusing a basic aqueous solution. Also, oxetane undergoes a ring-openingpolymerization under a certain condition and causes also a decrease ofsolubility as a result of increase of the molecular weight, which takesplace as a result of the cross-linking reaction of the resin.Furthermore, the foregoing reaction causes regeneration of protonicacid, and the chemical amplification reaction achieves a highsensitivity. In the present invention, the pattern formation is achievedprimarily by the polarity change, and a pattern having no swelling isobtained.

Also, with respect to the alkaline-soluble polymer used for the baseresin in the resist composition of the present invention, a firstmonomer unit of the copolymer may have a strong alkaline-soluble groupsuch as a carboxyl group and a second monomer unit may have weakalkaline-soluble group such as the one having a lactone stricture, anacid anhydride, and an imide-ring structure, and the like, particularlywhen the polymer is a three-component copolymer. In this case, itbecomes easy to control the rate of dissolution of the base resin to analkali to a preferred value by controlling the contents of the strongalkaline-soluble group and the weak alkaline-soluble group. Also, it ispossible to use a functional group having an etching-resistance for athird monomer unit. This is most preferable for a resist.

In the resist composition according to the present invention, thestructure of the alkaline-soluble polymer used for the base resin is notparticularly limited as far as the above mentioned conditions,particularly the condition of realizing a proper rate of dissolution toalkali is satisfied. However, in view of obtaining a dry-etchingresistance similar to that of Novolak, a polymer consisting of anacrylate monomer unit and/or a methacrylate monomer unit, in which anester bond is bonded to a polycyclic alicyclic hydrocarbon structure, avinylphenol polymer, a N-substituted maleimide polymer, a styrenepolymer, and a norbornene polymer, etc. are recommended. When an opticalsource of deep ultraviolet radiations, especially a source emittingradiation with the wavelength of 250 nm or less is used as for theexposure source, an acrylate polymer, a methacrylate polymer, and anorbornene polymer become important due to small absorbance ofradiations in this wavelength range. In other words, when a source ofdeep ultraviolet radiation is used as for an exposure source, it isdesirable to employ a polymer having a structure not to contain anaromatic ring, which generally absorbs the radiation substantially atthe ultraviolet region, or a chromophore having a large molar absorbancecoefficient such as a conjugated double bond, and the like.

When a source of exposure radiation having a short wavelength spectralregion such as an ArF excimer laser is used, the use of a polymer havingan ester bond bonding to a polycyclic alicyclic hydrocarbon structurerepresented by an adamantyl group or a norbornyl group, which has highdry-etching resistance described above is recommended. Paricularly, anacrylate polymer, a methacrylate polymer, and a norbornene polymer arerecommended because of the requirement of transparency to the wavelengthof the exposure radiation (193 nm) and because of the dry-etchingresistance.

Further, in the case of using a vacuum ultraviolet light such as F₂laser (wavelength 157 nm) for the radiation source, it is more difficultto maintain the transparency. Thus, combination of fluorine-containingresin represented by a norbornene fluoride polymer and a vinylfluoridepolymer is recommended. Alternately, the use of an oxetane structure forthe side chain of the unit containing a fluorine unit is recommended.

Although the molecular weight (weight-averaged molecular weight: Mw) ofthe polymers described above or other alkaline-soluble polymers can bevaried in a wide range, preferably it is in the range from 2,000 to 1million, more preferably in the range of 3,000 to 50,000.

The alkaline-soluble polymers that can be advantageously used inimplementation of the present invention, while not being limited to thefollowing materials, comprise the following. It should be noted that l,m, and n in the formula represent the number of monomer units (repeatunits) necessary to obtain the weight-averaged molecular weightdescribed above, while R₁, R₂ and R₃ represent arbitrary substituentssuch as a hydrogen atom, halogen atoms (a chlorine atom and a bromineatom, etc.), lower alkyl groups (a methyl group and an ethyl group,etc.), a cyano group, a fuluoro lower alkyl group and others, andidentical to or different from each other, unless otherwise noted.

(1) An acrylate polymer or a methacrylate polymer

In the structural formula, R₄ is, for example, a weak alkaline-solublegroup represented by a lactone ring. However, the monomer unit includingR₄ is elective, as far as rate of dissolution exhibits proper value asfor a substrate of the negative resist. R₅ is a unit having an oxetanestructure.

In addition, the alkaline-soluble polymer may be one having a structurecontaining an ester bond bonding to a carboxyl group being analkaline-soluble group as follows.

In the above structure, R₄ is defined in common with the previousformula. Both R₆ and R₇ are H atom or an oxetane structure. However theyare not the same structure (both H atoms or both oxetane structures).Although R_(x) may be an arbitrary structure, a polycyclic alicyclicstructure is preferred.

(2) A polymer containing a styrene-based unit as an alkaline-solublepolymer as follows

In the structural Formulas, Ry is an arbitrary substituent. It ispreferable for Rx to be selected similar to the above mentioned.

(3) A polymer containing a fumaric acid-based unit as follows

(4) A polymer containing a vinylbenzoic acid-based unit as follows

(5) A polymer containing a norbornene-based unit and a derivativethereof as follows

In these structural formulas, p and q are integers of from 0 to 4respectively, and identical to or different from each other.

(6) A polymer containing an itaconic acid-based unit as follows

(7) A polymer containing a maleic acid-based unit as follows

(8) A polymer containing a vinylphenol-based unit as follows

(9) A polymer containing a tetracyclododecanyl-based unit as follows

The polymers may be combined with other appropriate monomers to form anarbitrary copolymer (including a copolymer containing equal to or morethan three components) as aforementioned.

As further illustrated in detail, an alkaline-soluble polymer usableadvantageously in implementation of the present invention is, forexample, the materials shown below.

In the above formula, RR is, for example, a substituent as follows.

The embodiments illustrated above are merely examples, and the polymersaccording to the present invention is not limited to the structuresdescribed above. In the formula, R_(y) and R₅ are explained before.

In the above structural formula, functional groups advantageously usedas for R₅, includes, for example, the following structures.

In oxetanes represented by the above formula, g is an integer of from 0to 4, and X is a hydrogen atom (H) or an alkyl group having 8 or lesscarbon atoms of which the structure may be a straight chain or abranched chain and may include a ring.

In oxetanes represented by the above formula, definitions of R_(x) and Xare described above.

The above mentioned alkaline-soluble polymer can be prepared by usingpolymerization methods generally utilized in the art of polymerchemistry. For example, a certain monomer component can beadvantageously prepared by heating under the presence of AIBN(2,2′-azobisisobutyronitrile), etc. as for a free radical initiator.Also, an alkaline-soluble polymer except a methacrylate-based polymercan be advantageously prepared similarly by an ordinary method.

In the structure of the resin having high transparency at the deepultraviolet spectral region or in the additional compound containing anoxetane structure, a high sensitive resist suitable for exposure withdeep ultraviolet radiations is obtained, provided that the structure ofthe resin or the compound is selected properly such that no chromophorehaving a large molar absorption coefficient in the spectral region offrom 150 to 250 nm is contained.

As illustrated before, an oxetane structure performs a ring-openreaction under a certain condition and reacts with an alkaline-solublegroup such as a carboxyl group. That is, an oxetane works as across-linking agent in the resin under coexistence of analkaline-soluble resin, and causes the resin to be insolubilized by theincrease of the molecular weight of the alkaline-soluble resin. Fromthis reason, the inventors have conceived that the composition includingan alkaline-soluble group and an oxetane structure would form a negativeresist. Further, an oxetane performs cationic polymerization under acertain condition. Therefore, when a compound containing an oxetanestructure shows alkaline-solubility, the alkaline-solubility is lost bycationic polymerization, and the exposed area of the resist isselectively insolubilized. In this way, the inventors also conceivedthat these compositions would become a negative resist.

In the resist composition according to the present invention, astructure of an alkaline-soluble resin is not limited as far as theresin contains an alkaline-soluble group as described above. As for asingle layer resist composition, a phenol resin, an acrylate resin,which are generally used as for the base resin, and a copolymer thereof,and furthermore a silicon-containing resin containing a carboxyl group,a phenolic hydroxide group, and hexafluorocarbihol, etc. can be used.Preferably, a silicon-containing resin represented by the above formula(4) or (5) may be used.

The compound having an oxetane structure represented by the aboveformula (1) is not limited particularly. With respect to analkaline-soluble resin and a compound having an oxetane structure, aplural kinds of these may coexist as far as the above mentionedcondition is satisfied.

The resist composition according to the present invention becomes achemical amplification negative resist composition, provided that analkaline-soluble resin is employed as for the main agent, a compoundcontaining an oxetane structure, if necessary, is used as for thecross-linking agent, and an acid generator is added to the resin.

In the chemical amplification resist according to the present invention,as for a photoacid generator (PAG) used in combination with anacid-reactive polymer described above, a PAG generally used in the artof the resist chemistry can be used. That is, the PAG material generatesa protonic acid when it is illuminated with the radiation such asultraviolet radiation, far ultraviolet radiations, vacuum ultravioletradiations, electron beams, soft X-rays, X-rays, and the like. PAGsusable in the present invention include the following compounds,although it is not limited.

(1) Salts of onium ions(R″)₂—I⁺X⁻(R″)₃—S⁺X⁻

In the above formulas, R″ is a substituted or non-substituted aromaticring or alicyclic group and X is selected from the group consisting ofBF₄, PF₆, AsF₆, SbF₆, CF₃SO₃ and ClO₄, etc.

(2) Esters of Sulfonic Acid

(3) Halides

The PAGs are used in various amounts in the resist composition accordingto the present invention. A content of a PAG is preferably from 0.1 to50% by weight (percentage to weight of a polymer) and more preferablyfrom 1 to 15% by weight. With respect to the resist compositionaccording to the present invention, particularly, it is preferable todetermine structures of a polymer and a PAG and a content of the PAG inorder that absorbance at wavelength of exposed light is equal to or lessthan 1.75.

The resist composition according to the present invention isadvantageously utilized as a resist solution prepared by dissolving theabove mentioned alkaline-soluble polymer and a PAG in a proper organicsolvent. Organic solvents useful to prepare resist solution are ethyllactate, methyl amyl ketone, methyl-3-methoxypropionate,ethyl-3-ethoxypropionate, and propylene glycol methyl ether acetate,etc., and not limited to them. These solvents may be used independentlyand, if necessary, equal to or more than two kinds of the solvents maybe mixed each other and used. Moreover, although the content of thesolvent is not limited particularly, it is preferable to use the enoughquantity to obtain appropriate viscosity of the resist solution forcoating such as spin coating, etc. and desirable thickness of a resistfilm.

In the resist solution according to the present invention, if necessary,a supplementary solvent may be used in addition to the (main) solventdescribed above. A supplementary solvent may be not required dependenton solubility of a solute and uniformity for coating solution. When asolute having low solubility is employed or uniformity for coating doesnot satisfy desired condition, additional quantity of the supplementarysolvent is preferably from 1 to 30% by weight to a main solvent, andmore preferably from 10 to 20% by weight in common. Useful supplementarysolvents include, for example, butyl acetate, γ-butyrolactone andpropylene glycol methyl ether, etc., although they are not limited tothem.

The present invention also provides a method to form a resist pattern,particularly a negative resist pattern, on a substrate by using theabove mentioned resist composition. The negative resist patternaccording to the present invention can be formed as follows.

At first, the resist composition according to the present invention isapplied to a substrate to form a resist film. The substrate may be asubstrate generally used in a semiconductor device or another devicessuch as a MR head, and for example, a silicon substrate, a glasssubstrate, and non-magnetic ceramics substrate, etc. are given. Ifnecessary, an additional layer such as a silicon oxide layer, metallayer for wiring, an interlayer insulating film layer, and a magneticfilm, etc. may be laid and each kind of wiring or circuit may beproduced on the substrate. Furthermore, the substrate may behydrophobized by an ordinary method to improve adhesion of a resist filmto the substrate. As for the appropriate primer agent, for example,1,1,1,3,3,3-hexamethyldisilazane, etc. may be used.

For applying a resist composition, a resist solution described above canbe coated on a substrate. As for a method for coating a resist solution,although some ordinary methods such as spin coating, roll coating, anddip coating, etc., may be used, the spin coating is particularly useful.The thickness of the resist film of from 0.01 to 200 μm is recommended.In the case the resist is exposed by means of an excimer laser such asKrF, ArF or F₂ laser, the thickness of from 0.05 to 5 μm is recommended.The thickness of the formed resist film can be widely variedcorresponding to various factors such as purpose of the resist film.

It is preferable that the resist film applied on a substrate issubjected to a pre-baking process for the duration of 30 to 120 secondsat the temperature of 60 to 180° C. before the resist film is exposed tothe radiation for imaging. The pre-bake process can be implemented bymeans of a commonly used heating method. As for the suitable heatingmethod, for example, a hot plate, a heat oven with infrared radiation,or a heat oven with microwave may be employed.

After the pre-baking process, the resist film after is exposed to theradiation for imaging by using a commonly used exposure apparatus. Theexposure apparatus may be the one that uses an ultraviolet radiation, afar ultraviolet radiation, a deep ultraviolet radiation, or a vacuumultraviolet radiation, an X-ray, an electron beam, or suitable radiationavailable from the market. Particularly, the above mentioned excimerlasers (a KrF laser at the wavelength of 248 nm, an ArF laser at thewavelength of 193 nm, or a F₂ laser at the wavelength of 157 nm) may beadvantageously used as for the exposure light source in the presentinvention. It should be noted that the term “radiation” as used in thespecification includes any radiation originating from any kinds of lightsources.

After the exposure process, a protection reaction of an alkaline-solublegroup is caused by conducting a PEB (post-exposure bake) process on theexposed resist film under the presence of the acid catalyst. Thepost-exposure baking may be carried out similarly to the case of thepre-baking process explained previously as far as the protectionreaction is caused with sufficient degree. For example, the PEB can becarried out for an interval of 30 to about 120 seconds at thetemperature of 60 to 180° C. It is particularly preferable that thebaking condition is adjusted according to the desired pattern size andform.

After the PEB is performed, the resist film is developed with a basicaqueous solution used as a developer. For the development, a commonlyused development apparatus such as a spin developer, a dip developer ora spray developer may be used. In the case a basic aqueous solution isused for the developer, a solution of a metal hydroxide containing ametal classified to group I or group II in the periodic table, such aspotassium hydroxide may be used. Alternatively, a solution of an organicbase not containing a metal ion such as tetraalkylammonium hydroxide maybe used. Particularly, a solution of tetramethylammonium hydroxide(TMAH) is most preferable, and an additive such as a surfactant mayadded for improving the development effect. As a result of thedevelopment, the unexposed area of the resist film is dissolved andremoved, while the exposed area remains on the substrate and forms anegative resist pattern.

The foregoing method of forming a resist pattern of the presentinvention can be applied to a multi-layer resist process as well as theabove mentioned single layer resist process. Thus, a negative resistpattern having high aspect ratio is formed on the substrate by using theresist composition of the present invention.

For example, the formation of a negative resist pattern by a bilayerresist process can be implemented according to the following procedure.

First, a first resist composition is applied on the substrate to form alower layer resist film, and the resist composition according to thepresent invention is applied on the lower layer resist film to form anupper layer resist. The upper layer resist film is then exposed to theradiation for imaging, and the exposed upper layer resist film isdeveloped with a basic aqueous solution to form a resist pattern,Further, the underlying lower layer resist film on the substrate isetched by using the resist pattern as a mask.

Thereby, the resist pattern on the upper layer is transferred to thelower layer resist film and a resist pattern having a high aspect ratiois obtained by both the lower layer resist film and the upper layerresist film.

More specifically, it is possible to use a conventional, generally usedorganic material, for the resist composition of the lower resist layer.Thus, it is preferred to use a commercially available resist materialsuch as a novolak resin, a poly(vinyl phenol) resin, and a conductivematerial based on polyaniline and polythiophene for this purpose. Thethickness of the lower resist layer is preferably between 0.1 and 10 μm,more preferably between 0.2 and 1.0 μm.

When applying the resist composition of the present invention, a solventmay be used according to the needs as described above. The solvent andthe applying method of the resist composition are the same as describedabove. The thickness of the resist composition is preferably set between0.03 and 1.0 μm, more preferably between 0.05 and 0.2 μm.

The exposure process and development process are implemented alsoaccording to the process explained above. At the time of etching thelower resist layer is etched, a plasma etching process conducted in aoxygen-containing atmosphere may be used. More particularly, the etchinggas may comprise oxygen and sulfur oxide. As the plasma etchingapparatus, it is possible to use a high-density plasma etchingapparatus.

EXAMPLES

The present invention will now be described in greater detail withreference to examples given below. It should be noted that thedescription hereinafter is no more than examples and is not construed aslimiting the invention. In the following examples, explanation will bemade on the synthesis method of alkaline-soluble polymers, preparationmethod the of resist compositions, formation method of the resistpatterns, and fabricating method of the semiconductor devices.

Example 1

Synthesis of poly(2-oxetanepropyl methacrylate-co-3-carboxyadamantylmethacrylate)

2.14 g (12.57 mmol) of 2-oxetanepropyl methacrylate, 6.15 g (23.35 mmol)of 3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon(trademark), 24 ml of dioxane, and 885 mg (5.39 mmol) ofazobisisobutyronitrile (AIBN) were provided in a 100 ml eggplant-shapeflask and stirring was made for 7 hours at 70° C. under nitrogenatmosphere. The reaction solution was diluted with THF. The obtainedsolution was dropped to 11 of diethyl ether containing small amount ofhydroquinone and a precipitate was produced. The precipitate wasfiltrated through a glass filter and dried for 6 hours at 45° C. and 0.1mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated twice,to obtain a white powder of a resin with a yield of 6.05 g (73%). Thecopolymerization ratio of the oxetane to the adamantyl was proved to be64:36 by means of ¹H NMR. The weight-averaged molecular weight of theresin was 13,400 and the degree of the dispersion was 1.43.

Example 2

Synthesis of poly(2-oxetanebutyl methacrylate-co-3-carboxyadamantylmethacrylate) (see the following formula)

2.32 g (12.57 mmol) of 2-oxetanebutyl methacrylate, 6.15 g (23.35 mmol)of 3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon, 24ml of dioxane, and 885 mg (5.39 mmol) of azobisisobutyronitrile (AIBN)were provided in a 100 ml eggplant-shape flask and stirring was made for7 hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 11 of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 6.95 g (82%). The copolymerization ratio of the oxetaneto the adamantyl was proved to be 65:35 by means of ¹H NMR. Theweight-averaged molecular weight of the resin was 15,800 and themolecular weight dispersion was 1.48.

Example 3

Synthesis of poly(methacrylicacid-co-3-(2′-oxetanepropyloxymethyl)adamantyl methacrylate) (see thefollowing formula)

1.09 g (12.57 mmol) of methacrylic acid, 7.81 g (23.35 mmol) of3-(2′-oxetanepropyloxymethyl)adamantyl methacrylate, a stirrer barcoated with Teflon, 0.15.5 ml of dioxane, and 885 mg (5.39 mmol) ofazobisisobutyronitrile (AIBN) were provided in a 100 ml eggplant-shapeflask and stirring was made for 7 hours at 70° C. under nitrogenatmosphere. The reaction solution was diluted with THF. The obtainedsolution was dropped to 11 of diethyl ether containing small amount ofhydroquinone and a precipitate was produced. The precipitate wasfiltrated through a glass filter and dried for 6 hours at 45° C. and 0.1mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated twice,to obtain a white powder of a resin with a yield of 5.7.9 g (65%). Thecopolymerization ratio of the methacrylic acid to the adamantyl wasproved to be 36:64 by means of ¹H NMR. The weight-averaged molecularweight of the resin was 9,200 and the molecular weight dispersion was1.50.

Example 4

Synthesis of poly(2-oxetanepropyl acrylate-co-carboxytetracyclododecylacrylate) (see the following formula)

2.08 g (13.33 mmol) of 2-oxetanepropyl acrylate, 5.05 g (20 mmol) ofcarboxytetracyclododecyl acrylate, a stirrer bar coated with Teflon,11.1 ml of dioxane, and 821 mg (5 mmol) of azobisisobutyronitrile (AIBN)were provided in a 100 ml eggplant-shape flask and stirring was made for7 hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 600 ml of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 4.88 g (68.5%). The copolymerization ratio of theoxetane to the dodecyl was proved to be 66:34 by means of ¹H NMR. Theweight-averaged molecular weight of the resin was 10,900 and themolecular weight dispersion was 1.42.

Example 5

Synthesis of poly(2-oxetanebutylmethacrylate-co-3-methoxycarbonyladamantylmethacrylate-co-3-carboxyadamantyl methacrylate) (see the followingformula)

2.95 g (16 mmol) of 2-oxetanebutyl methacrylate, 0.2.78 g (10 mmol) of3-methoxycarbonyladamantyl methacrylate, 3.7 g (14 mmol) of3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon, 40 mlof dioxane, and 1.97 g (12 mmol) of azobisisobutyronitrile (AIBN) wereprovided in a 100 ml eggplant-shape flask and stirring was made for 7hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 11 of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 7.07 g (75%). The copolymerization ratio of the oxetane,the methoxycarbonyladamantyl, and the carboxyadamantyl was proved to be53:13:34 by means of ¹H NMR. The weight-averaged molecular weight of theresin was 19,500 and the molecular weight dispersion was 1.52.

Example 6

Synthesis of poly(2-oxetanepropylmethacrylate-co-5-norbornane-2,6-carbolactonemethacrylate-co-3-carboxyadamantyl methacrylate) (see the followingformula)

3.40 g (20 mmol) of 2-oxetanepropyl methacrylate, 1.33 g (6 mmol) of5-norbornane-2,6-carbolactone methacrylate, 3.7 g (14 mmol) of3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon, 40 mlof dioxane, and 1.97 g (12 mmol) of azobisisobutyronitrile (AIBN) wereprovided in a 100 ml eggplant-shape flask and stirring was made for 7hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 11 of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 5.41 g (58%). The copolymerization ratio of the oxetane,the norbonyl, and the adamantyl was proved to be 55:11:34 by means of ¹HNMR. The weight-averaged molecular weight of the resin was 18,700 andthe molecular weight dispersion was 1.49.

Example 7

Synthesis of poly(3-(2′-oxetanepropyloxy)adamantylacrylate-co-3-carboxyadamantyl acrylate) (see the following formula)

3.06 g (10 mmol) of 3-(2′-oxetanepropyloxy)adamantyl acrylate, 1.25 g (5mmol) of 3-carboxyadamantyl acrylate, a stirrer bar coated with Teflon,10 ml of dioxane, and 369 mg (2.25 mmol) of azobisisobutyronitrile(AIBN) were provided in a 100 ml eggplant-shape flask and stirring wasmade for 7 hours at 70° C. under nitrogen atmosphere. The reactionsolution was diluted with THF. The obtained solution was dropped to 500ml of diethyl ether containing small amount of hydroquinone and aprecipitate was produced. The precipitate was filtrated through a glassfilter and dried for 6 hours at 45° C. and 0.1 mmHg. The obtained whitepowder was dissolved to THF again and the precipitation and dryingprocesses described above were repeated twice, to obtain a white powderof a resin with a yield of 2.34 g (55%). The copolymerization ratio ofthe oxetane to the carboxyadamantyl was proved to be 64:36 by means of¹H NMR. The weight-averaged molecular weight of the resin was 18,200 andthe molecular weight dispersion was 1.41.

Example 8

Synthesis of poly(2-oxetanepropyloxynorbornene-co-maleicanhydride-co-1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropylnorbornene)(see the following formula)

1.92 g (10 mmol) of 2-oxetanepropyloxynorbornene, 0.98 g (10 mmol) ofmaleic anhydride, 2.62 g (10 mmol) of1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropylnorbornene, a stirrerbar coated with Teflon, 20 ml of dioxane, and 493 mg (3 mmol) ofazobisisobutyronitrile (AIBN) were provided in a 100 ml eggplant-shapeflask and stirring was made for 7 hours at 70° C. under nitrogenatmosphere. The reaction solution was diluted with THF. The obtainedsolution was dropped to 11 of diethyl ether containing small amount ofhydroquinone and a precipitate was produced. The precipitate wasfiltrated through a glass filter and dried for 6 hours at 45° C. and 0.1mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated twice,to obtain a white powder of a resin with a yield of 3.42 g (62%). Thecomposition ratio of the monomer units was proved to be 1:1:1 by meansof ¹H NMR. The weight-averaged molecular weight of the resin was 9,400and the molecular weight dispersion was 1.33.

Example 9

Synthesis of poly(2-oxetanepropyl methacrylate-co-maleicanhydride-co-norbornenecarboxylic acid) (see the following formula)

1.70 g (10 mmol) of 2-oxetanepropyl methacrylate, 0.98 g (10 mmol) ofmaleic anhydride, 1.38 g (10 mmol) of norbornenecarboxylic acid, astirrer bar coated with Teflon, 20 ml of dioxane, and 493 mg (3 mmol) ofazobisisobutyronitrile (AIBN) were provided in a 100 ml eggplant-shapeflask and stirring was made for 7 hours at 70° C. under nitrogenatmosphere. The reaction solution was diluted with THF. The obtainedsolution was dropped to 11 of diethyl ether containing small amount ofhydroquinone and a precipitate was produced. The precipitate wasfiltrated through a glass filter and dried for 6 hours at 45° C. and 0.1mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated twice,to obtain a white powder of a resin with a yield of 2.35 g (58%). Thecomposition ratio of the monomer units was proved to be 1:1:1 by meansof ¹H NMR. The weight-averaged molecular weight of the resin was 9,100and the molecular weight dispersion was 1.44.

Example 10

Synthesis of poly(2-oxetanebutyl acrylate-co-hydroxystyrene) (see thefollowing formula)

410 mg (2.41 mmol) of 2-oxetanebutyl acrylate, 4.66 g (27.75 mmol) ofacetoxystyrene, a stirrer bar coated with Teflon, 10 ml of dioxane, and743 mg (4.5 mmol) of azobisisobutyronitrile (AIBN) were provided in a100 ml eggplant-shape flask and stirring was made for 7 hours at 70° C.under nitrogen atmosphere. The reaction solution was diluted with THF.The obtained solution was dropped to 11 of methanol containing smallamount of hydroquinone and a precipitate was produced. The precipitatewas filtrated through a glass filter and dried for 6 hours at 45° C. and0.1 mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated, toobtain a white powder of a resin. The white powder was treated withbasic methanol solution to obtain a desired resin with a yield of 2.8 g.The composition ratio of the oxetane to the hydroxystyrene was proved tobe 92:8 by means of ¹H NMR. The weight-averaged molecular weight of theresin was 7,800 and the molecular weight dispersion was 1.33.

Example 11

Synthesis of poly(2-oxetanepropylmethacrylate-co-3,4-carbolactoneadamantylmethacrylate-co-3-carboxyadamantyl methacrylate) (see the followingformula)

3.40 g (20 mmol) of 2-oxetanepropyl methacrylate, 1.66 g (6 mmol) of3,4-carbolactoneadamantyl methacrylate, 3.7 g (14 mmol) of3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon, 40 mlof dioxane, and 1.97 g (12 mmol) of azobisisobutyronitrile (AIBN) wereprovided in a 100 ml eggplant-shape flask and stirring was made for 7hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 11 of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 5.26 g (60%). The copolymerization ratio of the oxetane,the lactone, the adamantyl was proved to be 52:15:33 by means of ¹H NMR.The weight-averaged molecular weight of the resin was 17,100 and themolecular weight dispersion was 1.41.

Example 12

Synthesis of poly(3-(2-oxetanepropyloxy)adamantylmethacrylate-co-3,4-carbolactoneadamantylmethacrylate-co-3-carboxyadamantyl methacrylate) (see, the followingformula)

6.17 g (20 mmol) of 3-(2-oxetanepropyloxy)adamantyl methacrylate, 1.66 g(6 mmol) of 3,4-carbolactoneadamantyl methacrylate, 3.7 g (14 mmol) of3-carboxyadamantyl methacrylate, a stirrer bar coated with Teflon, 40 mlof dioxane, and 1.97 g (12 mmol) of azobisisobutyronitrile (AIBN) wereprovided in a 100 ml eggplant-shape flask and stirring was made for 7hours at 70° C. under nitrogen atmosphere. The reaction solution wasdiluted with THF. The obtained solution was dropped to 11 of diethylether containing small amount of hydroquinone and a precipitate wasproduced. The precipitate was filtrated through a glass filter and driedfor 6 hours at 45° C. and 0.1 mmHg. The obtained white powder wasdissolved to THF again and the precipitation and drying processesdescribed above were repeated twice, to obtain a white powder of a resinwith a yield of 8.88 g (77%). The copolymerization ratio of the oxetane,the lactone, the adamantyl was proved to be 54:12:34 by means of ¹H NMR.The weight-averaged molecular weight of the resin was 21,000 and themolecular weight dispersion was 1.47.

Example 13

Synthesis of poly(3-(2-oxetanebutyloxy)adamantylmethacrylate-co-N-hydroxymethacrylamide-co-methacrylic acid) (see thefollowing formula)

4.82 g (16 mmol) of 3-(2-oxetanebutyloxy)adamantyl methacrylate, 2.02 g(6 mmol) of N-hydroxymethacrylamide, 861 mg (10 mmol) of methacrylicacid, a stirrer bar coated with Teflon, 20 ml of dioxane, and 788 mg(4.8 mmol) of azobisisobutyronitrile (AIBN) were provided in a 100 mleggplant-shape flask and stirring was made for 7 hours at 70° C. undernitrogen atmosphere. The reaction solution was diluted with THF. Theobtained solution was dropped to 11 of diethyl ether containing smallamount of hydroquinone and a precipitate was produced. The precipitatewas filtrated through a glass filter and dried for 6 hours at 45° C. and0.1 mmHg. The obtained white powder was dissolved to THF again and theprecipitation and drying processes described above were repeated twice,to obtain a white powder of a resin with a yield of 4.47 g (58%). Thecopolymerization ratio of the adamantyl, the amide, the methacrylic acidwas proved to be 65:5:30 by means of ¹H NMR. The weight-averagedmolecular weight of the resin was 9,900 and the molecular weightdispersion was 1.52.

Example 14

The resin synthesized in example 1 was dissolved in EL (ethyl lactate)to prepare 13% by weight of a solution. Herein, the solution alsocontained 10% by weight of γ-butyrolactone as a supplementary solvent.2% by weight of triphenylsulfonium trifluoromethanesulfonate was addedand sufficiently dissolved to the obtained solution. After the obtainedresist solution was filtrated through the Teflon membrane filter with0.2 μm mesh, the filtrated solution was coated on a substrate subjectedto HMDS treatment by means of spin-coating and pre-bake for 60 minutesat 110° C. to form a resist film with thickness of 0.4 μm. After theresist film was exposed by means of a KrF eximer laser stepper(NA=0.45), the film was baked for 60 minutes at 120° C., developed with2.38% of tetramethylammomium hydroxide (TMAH) as a developer, and rinsedwith a deionized water. 0.25 μm L/S of the resist pattern could beresolved in the condition of 17.0 mJ/cm² of the light exposure.

Example 15

A resist film with thickness of 0.4 μm was formed using the resistsynthesized in example 14. After the resist film was exposed by means ofa ArF excimer laser stepper (NA=0.60), the film was baked for 60 minutesat 120° C., developed with 2.38% of a TMAH developer, and rinsed with adeionized water. 0.15 μm L/S of the resist pattern could be resolved inthe condition of 9.0 mJ/cm² of the light exposure.

Example 16

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 2 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA-0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 12.0 mJ/cm² of the light exposure.

Example 17

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 3 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 11 mJ/cm² of the light exposure.

Example 18

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 4 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 14 mJ/cm² of the light exposure.

Example 19

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 5 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 8 mJ/cm² of the light exposure.

Example 20

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 6 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 9 mJ/cm² of the light exposure.

Example 21

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 7 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 8 mJ/cm² of the light exposure.

Example 22

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 6 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 18 mJ/cm² of the light exposure.

Example 23

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 6 in the manner as similar to that in example 14.After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 14 mJ/cm² of the light exposure.

Example 24

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 10 in the manner as similar to that in example14. After the resist film was exposed by means of a KrF excimer laserstepper (NA=0.68), the film was baked for 60 minutes at 110° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.18 μm L/S of the resist pattern could be resolved in thecondition of 13 mJ/cm² of the light exposure.

Example 25

A resist was prepared by adding 10% by weight of poly(2-oxetanepropylmethacrylate) (molecular weight: 5,600) to poly(hydroxystyrene) followedby dissolution in EL. After a resist film with thickness of 0.4 μm wasformed and exposed by means of a KrF excimer laser stepper (NA=0.68),the film was baked for 60 minutes at 110° C., developed with 2.38% of aTMAH developer, and rinsed with a deionized water. 0.22 μm L/S of theresist pattern could be resolved in the condition of 15 mJ/cm² of thelight exposure.

Example 26

A resist was prepared by adding 12% by weight of poly(2-oxetanepropylmethacrylate) (molecular weight: 5,600) to the resin represented by theabove structural formula (molecular weight: 9,500) followed bydissolution in EL. After a resist film with thickness of 0.4 μm wasformed and exposed by means of a ArF excimer laser stepper (NA=0.60),the film was baked for 60 minutes at 110° C., developed with 2.38% of aTMAH developer, and rinsed with a deionized water. 0.16 μm L/S of theresist pattern could be resolved in the condition of 17 mJ/cm² of thelight exposure.

Example 27

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 11 in the manner as similar to that in example14. After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 13 mJ/cm² of the light exposure.

Example 28

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 12 in the manner as similar to that in example14. After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 12 mJ/cm² of the light exposure.

Example 29

A resist film with thickness of 0.4 μm was formed using the resinsynthesized in example 13 in the manner as similar to that in example14. After the resist film was exposed by means of a ArF excimer laserstepper (NA=0.60), the film was baked for 60 minutes at 120° C.,developed with 2.38% of a TMAH developer, and rinsed with a deionizedwater. 0.15 μm L/S of the resist pattern could be resolved in thecondition of 18 mJ/cm² of the light exposure.

Example 30

A resist film with thickness of lam was formed on a silicon substrateusing the resist synthesized in examples 5, 7, 8, 10, 26 and 28. Forcomparison, PMMA (poly(methyl methacrylate)) and PFI-16 (provided fromSumitomo Chemical), which are commercially available novolac resists,were etched for 5 minutes under the condition of Pμ=200W, pressure=0.02Torr, and CF₄ gas=100 sccm in a parallel flat plate type RIE apparatus.The amounts of decrease of the sample films were compared and theresults listed in following table 1 were obtained. TABLE 1 Etching rateResist (A/s) Ratio of rate PFI-16 510 1.00 PMMA 760 1.49 Example 5 6221.22 Example 7 495 0.97 Example 8 612 1.20 Example 10 561 1.10 Example26 627 1.23 Example 28 479 0.94

As the result listed in above table 1, etching resistance of the resistaccording the present invention was similar to that of the novolacresists. Particularly, the resists described in examples 7 and 28 hadcompositions available against ArF exposure and resistance more thanthat of the novolac resists. From the experiment, it was confirmed thatall resists were very superior to PMMA. Also, occurrence of swelling wasnot found in a resist pattern in examples 5, 7, 8, 10, 26 and 28.

Example 31

Synthesis of a silicon-containing resin

To a four-neck flask provided with a condenser and a thermometer 6.9 g(0.023 mole) of 1,3-bis(carboxypropyl)tetramethyldisiloxane, 35 ml of apurified water and 20.6 ml of acetic acid were added under nitrogenatmosphere. The reaction mixture was stirred and raised to a temperatureof 60° C. in an oil bath. 12.48 g (0.06 mole) of tetraethoxysilane wasadded to the mixture dropwise for 30 minutes and the mixture was reactedfor one hour. 6.24 g (0.03 mole) of tetraethoxysilane was then added tothe mixture for 30 minutes and the mixture was reacted for 3 hours.After the reaction mixture was cooled to room temperature, the reactionsolution was transferred to a separatory funnel. 100 ml of water and 100ml of methyl isobutyl ketone (MIBK) were added to the separatory funneland solvent extraction was performed. An organic layer was filtratedwith a liquid layer separating filter paper and was transfer thefour-neck flask. Water was removed by azeotropic distillation to yield aMIBK solution containing a four-functional siloxane resin.

Next, to the four-neck flask equipped with the condenser and thethermometer, a half-concentrated MIBK solution and 100 ml oftetrahydrofuran was added and 12.0 g (0.84 mole) oftrimethylsilylimidazole was then added while stirring at roomtemperature. The mixture was reacted for two hours. 18 ml ofhydrochloric acid was added to the mixture and the reaction mixture wasfiltrated with the liquid layer separating filter paper and wastransferred into the four-neck flask. Water was removed by azeotropicdistillation. Freeze drying was carried out with dioxane for a componentwhich was precipitated with hexane after the solution had beenconcentrated, to give a desired silicon-containing resin having amolecular weight of 6,000 with a yield of 85%.

Example 32

100 parts by weight of the alkaline-soluble silicon-containing resinrepresented by formula (4) synthesized in example 31, 100 parts byweight of silicon-containing resin having the molecular weight of 3000and the oxetane structure represented by the following formula (5)(whichwas synthesized by a synthesizing method disclosed in Japanese Laid-OpenPatent Application No. 6-16804) and 5 parts by weight oftriphenylsulfonium triflate were dissolved in propylene glycolmonomethyl ether acetate (PGMEA) so as to prepare a resist solution.

The resist solution was spin-coated on a Si substrate which waspre-subjected to hexamethyldisilazane treatment and prebaking wasperformed at 100° C. for 60 seconds to form a resist film having thethickness of 0.14 μm. After exposing the resist film by means of the KrFexcimer laser stepper (NA=0.45), baking was carried out at 135° C. for60 seconds. Development of the resist film with 2.38% of TMAH resultedin formation of a line and space of 0.25 μm with an exposure amount of 7mJ/cm².

Example 33

100 parts by weight of the alkaline-soluble silicon-containing resinhaving the molecular weight of 6000 which is represented by formula (4)and was synthesized in example 31, 70 parts by weight ofsilicon-containing resin having the molecular weight of 3000 and theoxetane structure represented by the above formula (3) and 3 parts byweight of triphenylsulfonium triflate were dissolved in MIBK so as toprepare a resist solution.

First of all, a solution based on a novolak resin was spin-coated on theSi substrate and baking was carried out in an oven at 280° C. for 3hours to form the lower resist layer having the thickness of 0.4 μm. Theresist solution thus prepared above was then spin-coated on the lowerresist layer and prebaking was performed at 110° C. for 60 seconds toform the upper resist layer having the thickness of 0.1 μm. Afterexposure of the obtained resist layer having bilayer structure by meansof the ArF excimer laser exposing apparatus, baking was carried out at140° C. for 60 seconds. Development of the resist film with 2.38% ofTMAH resulted in formation of a line and space of 0.17 μm with anexposure amount of 10 mJ/cm².

Example 34

The upper pattern was transferred to the lower resist layer by means ofO₂-RIE using the upper resist pattern formed in Example 33 as the mask.The conditions of O₂-RIE is as follows: RF power; 0.16 W/cm², oxygenflow; 10 sccm, gas pressure; 10 mTorr. The results of etching rate isshown FIG. 1. Under these conditions O₂-RIE resistance of the upperresist was 100 times that of the lower resist. As a result, it wasconfirmed that a line and space pattern of 0.17 μm which was formed inthe upper resist layer was successfully transferred to the lower resistlayer without dimensional variation.

Example 35

100 parts by weight of the alkaline-soluble silicon-containing resinhaving the molecular weight of 6000 and being represented by the formula(4), 50 parts by weight of silicon-containing resin having the molecularweight of 3000 and the oxetane structure represented by the aboveformula (3) and 5 parts by weight of triphenylsulfonium triflate weredissolved in methyl isobutyl ketone (MIBK) so as to prepare a resistsolution.

As similar to example 33, the lower resist layer was formed on the Sisubstrate so that the thickness was 0.4 μm. Subsequently, the resistsolution thus prepared above was spin-coated on the lower resist layerand prebaking was carried out at 110° C. for 60 seconds to form theupper resist layer having the thickness of 0.1 μm. After exposure of theobtained resist layer having bilayer structure by means of the electronbeam exposing apparatus, baking was carried out at 135° C. for 60seconds and development of the resist film with 2.38% of TMAH aqueoussolution resulted in formation of a line and space of 0.125 μm with anexposure amount of 45 μC/cm².

Example 36

The upper pattern was transferred to the lower resist layer by means ofO₂-RIE using the upper resist pattern formed in Example 35 as the mask.Under the same conditions as in Example 34 O₂-RIE resistance of theupper resist was about 90 times that of the lower resist. As a result,it was confirmed that a line and space pattern of 0.125 μm which wasformed in the upper resist layer was successfully transferred to thelower resist layer without dimensional variation.

Example 37

A more specific method for fabricating the semiconductor device will bedescribed below using the resist composition according to the presentinvention.

FIGS. 2A-2C show a forming method of a wiring pattern of a gatenecessary for a high aspect ratio in order. An isolated MOS transistor10 is provided on a silicon substrate 1 by means of field oxidation. Aninsulating layer 21 is formed on a gate electrode 11 of the MOStransistor and an opening is formed by means of a lithographic means inorder to draw a wiring from the gate electrode 11. As a barrier metal, athin film 31 of titanium nitride (TiN) is then formed on the insulatinglayer 21 and a thin film 32 made from Al as a wiring material isdeposited on the TiN film (See, FIG. 2A).

In order to process this Al/TiN layers as the wiring pattern, a resistpattern 42 is formed thereon as an etching mask according to a proceduredescribed in Example 32. The obtained resist pattern is then transferredto a lower layer by means of an oxygen plasma etching method usingresist pattern 42 as the mask (See, FIG. 2B). Then, the resist pattern42 is then removed by fluorine-based plasma etching to form an etchingmask 41.

By use of the etching mask 41, the Al/TiN stacked layer is etched bymeans of chlorine-based plasma so as to provide a gate wiring patternhaving the high aspect ratio (See, FIG. 2C).

The present invention is not limited to the specifically disclosedembodiments, and variation and modifications may be made withoutdeparting from scope of the present invention.

The present invention is based on Japanese priority applications No.2000-089790 filed on Mar. 28, 2000, and No. 2001-093727 filed on Mar.28, 2001, the entire contents of which are hereby incorporated byreference.

1-16. (canceled)
 17. A method for forming a negative resist patterncomprising the steps of: applying a resist composition on a substrate toform a resist film, said resist composition containing analkaline-soluble resin as a base material, an oxetane structurerepresented by the following formula (1):

is contained in a structure of the alkaline-soluble resin or in astructure of a compound used in combination with the alkaline-solubleresin; exposing the resist film to a radiation used for imaging apattern; developing said exposed resist film with a basic aqueoussolution to form the negative resist pattern.
 18. The method for forminga negative resist pattern as claimed in claim 17, wherein said radiationused for imaging a pattern is a radiation capable of causing adissociation of a photoacid generator contained in said resistcomposition.
 19. A method for fabricating a semiconductor devicecomprising the steps of: applying a resist composition on a substrate toform a resist film, the resist composition containing analkaline-soluble resin as a base material, an oxetane structurerepresented by the following formula (1):

is contained in the structure of said alkaline-soluble resin or in thestructure of a compound used in combination with the alkaline-solubleresin; exposing said resist film to a radiation for imaging a pattern;developing the exposed resist film with a basic aqueous solution to forma negative resist pattern.
 20. A method for forming a negative resistpattern comprising the steps of: applying a first resist composition ona substrate to form a lower layer resist film; applying a second resistcomposition on said lower layer resist film to form an upper layerresist film, said second resist composition containing analkaline-soluble resin as a base material, an oxetane structurerepresented by the following formula (1):

is contained in the structure of said alkaline-soluble resin or in thestructure of a compound used in combination with said alkaline-solubleresin; exposing said upper layer resist film to radiation for imaging apattern; developing the exposed upper layer resist film with a basicaqueous solution to form a resist pattern; etching said lower layerresist film by using said resist pattern as a mask to form a negativeresist pattern by said lower resist film and said upper resist film.